1. Field of the Invention
The present invention relates to a chemical vapor deposition (CVD) apparatus and, more particularly, to a CVD apparatus for silicon epitaxial growth.
2. Description of the Related Art
A demand for Si epitaxial wafers (Si wafers with epitaxial films) has been enhanced to obtain high quality bipolar, Bi-CMOS, CCD and other semiconductor devices. Additionally, diameters of the Si wafers have become as large as 5 to 6 inches to reduce the process costs. However, since a wafer-processing capacity of the conventional CVD apparatus was small, a large number of Si wafers of large diameters could not be treated simultaneously, resulting in the expensive cost for manufacturing epitaxial wafers. Moreover, the uniform film thickness and the uniform crystal quality could not be obtained over the entire Si wafer of large diameter.
For improving a growth of the uniform epitaxial layer on the Si wafer of large diameter, a CVD apparatus was proposed in Japanese Laid open patent No. 62-173712. In this CVD apparatus, Si wafers having diameters of 6 inches were vertically stacked in a wafer holder. To obtain a uniformity of the epitaxial layers, the wafer holder was rotated so as to supply the starting gases on the Si wafers through holes of a gas-supply nozzle tube, the direction of the holes being deviated from the rotation center of each Si wafer. In this CVD apparatus, however, the number of the gas-supply nozzle tube was only one. Thus, the flow of the starting gases over the Si wafer was still nonuniform, especially over the Si wafer of a large diameter. Therefore, the obtained uniformity of the epitaxial layer does not have a level required for using for large-scale integrated circuits.